Donor-acceptor system introduces N defect modified g-C3N4 for efficient photocatalytic degradation of methylene blue under visible light

Abstract

The ability of photocatalysts to combat environmental pollution can be effectively improved by defect modulation. This paper developed a donor-acceptor (D-A) precursor system using urea as the hydrogen bond donor and cyanoacetic acid as the hydrogen bond acceptor to successfully synthesize modified g-C3N4 (CA-CNx). The results showed that while cyanoacetic acid addition contributed to the formation of N defects in g-C3N4, but cyanoacetic acid overuse caused structural disorder in CA-CNx. A decrease in the g-C3N4 band gap and an improvement in the photogenerated carrier mobilities due to the inclusion of N defects may lead to more effective usage of visible light. The highest catalytic activity for methylene blue (MB) solution (40 mg/L) was demonstrated by the modified g-C3N4 synthesized by adding 0.4 g cyanoacetic acid, and the degradation rate of the MB solution reached 90.4 % within 100 min. The proposed primary kinetic constant was 6.91 times higher than the original g-C3N4. According to free radical scavenging tests, superoxide radicals are the predominant active species during the catalytic breakdown of MB processes. This method provides a novel idea to producing g-C3N4 with N-defects and the opportunity to comprehend the impact of structural defects in enhancing semiconductor photocatalytic activity.